1. Field of the Invention
The present invention relates to a wafer carrier device which is to be installed in a wafer grinder.
2. Related Arts
A wafer grinder is designed to handle a cassette containing a plurality of wafers. After being ground, the wafers are put in the cassette to be transferred to the subsequent stage. For this purpose the wafer grinder is equipped with a wafer carrier device 50 for taking out wafers from a cassette and for putting the wafers in another cassette, as seen from FIG. 7.
The wafer carrier device comprises a bifurcate wafer holder 51 having suction areas 56 in its wafer-bearing area 55, an articulate arm-like extension 52 connected to the wafer holder 51, turning means 53 for rotating the arm-like extension 52, and elevating means 54 for raising and descending the arm-like extension 52. A wafer W is put on the bearing area 55, and is positively held by drawing air from the suction areas 56. Then, the wafer W is carried to a desired position with the aid of the arm-like extension 52, and turning and elevating means 52 and 53.
Each suction area 56 has a recess 0.5 millimeters deep, and the recess has a suction hole 57 made at its center, as seen from FIG. 8. The suction hole 57 communicates with a suction source (not shown). The suction hole is circular, and its diameter is for example, 3 millimeters long. The wafer W is laid on the bearing area 55 to be sucked by applying a negative pressure to the suction holes 57 from the suction source. Thus, the wafer W can be positively held on the bearing area 55.
As the recent tendency wafers are ground to minimum thickness; such thin wafers are required in the fields of cellular phones, personal computers and memory cards. Wafers are often ground to be 100 or less microns thick. When such a thin wafer W is sucked and pulled toward the center suction hole 57, it is liable that the wafer is bent badly as shown in FIG. 8, and that the wafer is broken sometimes.
One object of the present invention is to provide a wafer carrier which can hold by suction, and can transfer a thin wafer without fear of breaking the same.
To attain this object a wafer carrier device comprising a wafer holder having at least one suction area in its wafer-bearing area, an articulate arm-like extension connected to the wafer holder, turning means for rotating the arm-like extension is improved according to the present invention in that the suction area has a plurality of minute suction spots.
Each suction spot may be a pore whose diameter is 0.5 or less millimeters, and the number of such pores is 50 or more.
Each suction spot may be a minute groove whose width is 0.5 or less millimeters, and the number of such minute grooves is 20 or more.
The suction area may be of a piece of porous material.
The wafer holder may have wafer reversing means for turning the wafer up side down.
The minute suction spots cause dispersion of the stress applied to the wafer evenly over the whole suction area, thereby preventing the bending or breaking of the wafer.
Other objects and advantages of the present invention will be understood from the following description of a wafer carrier device according to one preferred embodiment of the present invention, which is shown in accompanying drawings.